Ultrasound diagnostic apparatuses are used in the medical field. An ultrasound diagnostic apparatus is an apparatus which transmits and receives ultrasound to and from a living body, and forms an ultrasound image based on a reception signal obtained by the transmission and reception of the ultrasound. The transmission and reception of the ultrasound to and from the living body are executed by an ultrasound probe (probe). The probe includes a transducer including a piezoelectric element, and ultrasound is transmitted and received by driving the piezoelectric element.
The transducer includes a matching layer placed on a living body side of the piezoelectric element. The matching layer is a layer for acoustically matching the piezoelectric element and the living body, by gradationally reducing an acoustic impedance from the piezoelectric element toward the living body. In addition, the transducer may include a resonance layer placed adjacent to a back surface of the piezoelectric element; that is, a surface opposite from the living body side. An acoustic impedance of the resonance is higher than that of the piezoelectric element, and is useful for resonating with the piezoelectric element to effectively transmit the ultrasound toward the living body. On a back surface of the transducer, a circuit board having an electronic circuit which drives the piezoelectric element is placed. Patent Document 1 shows an example of the ultrasound probe.